This invention relates to a gripping jaw. FR-A-2 373 351 discloses a chuck in the body of which there slides axially a traction rod that acts on a transmission system which converts the axial translation of this rod into a radial translation in terms of each jaw holder. These latter are provided with lateral flat bars which interact with flat bars recessed in the body in such a fashion as to guide the radial sliding of the jaw holders.
By means of this contrivance, the transmission of the clamping force of the rod on the jaws is exerted through inclined faces, and the distribution of the force is the same on each jaw. This generally satisfactory system can however present a drawback associated with the statically overdefined character of the clamping thus obtained. In fact, each jaw holder can swivel axially only very slightly, which means that the jaws are often only imperfectly moulded to the shape of the piece they are required to chuck.
Thus, in the case of components such as brake drums and disks, beating rings, flanges, flywheels or wheels, such a statically overdefined clamping can lead to appreciable deformations--which is unacceptable for precision pieces the dimensions of which are subjected to very exacting tolerances.